embedded: change the function representation of directly called witness methods #85707
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…onTypeRepresentation`
…tations when creating specialized functions
…e representation of a function
…original: Function)`
…ite.replace(withCallTo:)`
…ss methods This is needed in Embedded Swift because the `witness_method` convention requires passing the witness table to the callee. However, the witness table is not necessarily available. A witness table is only generated if an existential value of a protocol is created. This is a rare situation because only witness thunks have `witness_method` convention and those thunks are created as "transparent" functions, which means they are always inlined (after de-virtualization of a witness method call). However, inlining - even of transparent functions - can fail for some reasons. This change adds a new EmbeddedWitnessCallSpecialization pass: If a function with `witness_method` convention is directly called, the function is specialized by changing the convention to `method` and the call is replaced by a call to the specialized function: ``` %1 = function_ref @callee : $@convention(witness_method: P) (@guaranteed C) -> () %2 = apply %1(%0) : $@convention(witness_method: P) (@guaranteed C) -> () ... sil [ossa] @callee : $@convention(witness_method: P) (@guaranteed C) -> () { ... } ``` -> ``` %1 = function_ref @$e6calleeTfr9 : $@convention(method) (@guaranteed C) -> () %2 = apply %1(%0) : $@convention(method) (@guaranteed C) -> () ... // specialized callee sil shared [ossa] @$e6calleeTfr9 : $@convention(method) (@guaranteed C) -> () { ... } ``` Fixes a compiler crash rdar://165184147
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This is needed in Embedded Swift because the
witness_methodconvention requires passing the witness table to the callee.However, the witness table is not necessarily available.
A witness table is only generated if an existential value of a protocol is created.
This is a rare situation because only witness thunks have
witness_methodconvention and those thunks are created as "transparent" functions, which means they are always inlined (after de-virtualization of a witness method call).However, inlining - even of transparent functions - can fail for some reasons.
This change adds a new EmbeddedWitnessCallSpecialization pass:
If a function with
witness_methodconvention is directly called, the function is specialized by changing the convention tomethodand the call is replaced by a call to the specialized function:->
Fixes a compiler crash
rdar://165184147